1. Field of the Invention
The present invention relates to a rubber composition, and to a hose including the rubber composition and having a brass-plated wire as a reinforcing layer. More specifically, the present invention relates to a hose having high adhesion to a brass-plated wire and having excellent heat resistance, low-temperature resistance, and oil resistance.
2. Description of the Related Art
A high-pressure hose using a brass-plated wire as a reinforcing layer generally has an inner tube including acrylonitrile-butadiene copolymer rubber (NBR) and an outer cover including chloroprene rubber (CR) in the case where the hose is intended to be used at a temperature of 100° C. or lower. Meanwhile, in the case where the hose is intended to be used at a temperature of higher than 100° C., it generally has an inner tube including hydrogenated acrylonitrile-butadiene copolymer rubber (HNBR) and an outer cover including ethylene-propylene-diene copolymer rubber (EPT), chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene rubber (CPE), or the like.
However, EPT has poor oil resistance, so it is not suitable for a hose to be used in a hydraulic circuit. On the other hand, CSM and CPE each include chlorine in the rubbers, so a wire is easy to corrode when the rubbers are used at high temperature. In particular, in the case of CSM, lead oxide is effective for corrosion prevention (see JP 07-196866 A, Claims), but use of lead compounds tends to be restrained because of environmental problems, and it has been required to develop a rubber composition having heat resistance and oil resistance as an alternative to chlorine-containing rubbers.
Acrylic rubber and ethylene-(meth) acrylate copolymer rubber (AEM) have been proposed as alternatives to the above-mentioned chlorine rubbers, but the acrylic rubber which has a chlorine active group and is easy to adhere to a brass-plated wire has a problem of easily corroding the brass-plated wire as in the case of CSM or CPE and having poor low-temperature resistance. Meanwhile, AEM has relatively good low-temperature resistance, but has a problem of having low adhesion to a brass-plated wire.
To solve the above-mentioned problems, there has been proposed a hose including a rubber composition containing hydrogenated acrylonitrile-butadiene copolymer rubber, ethylene-acrylate copolymer rubber, an organic peroxide to be used for rubber crosslinking, a triazine compound as a vulcanizer, and a polymer having an epoxy group which is crosslikable by an organic peroxide (see JP 2001-241573A, Claims, and Example 1). The rubber composition containing the polymer having an epoxy group has excellent adhesion to a brass-plated wire, heat resistance, and the like, but it has problems of having high viscosity, resulting in poor workability in milling and extrusion.